Lissamphibia

Lissamphibia Temporal range: Early Triassic – Present (Possible Cisuralian record) PreꞒ Ꞓ O S D C P T J K Pg N
Emerald glass frog (Centrolene prosoblepon)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Subclass:	Lissamphibia Haeckel, 1866
Subgroups
†Allocaudata Batrachia Gymnophiona

The Lissamphibia (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians") is a group of

For several decades, this name has been used for a group that includes all living amphibians, but excludes all the main groups of Paleozoic tetrapods, such as Temnospondyli, Lepospondyli, Embolomeri, and Seymouriamorpha.^[1] Most scientists have concluded that all of the primary groups of modern amphibians—frogs, salamanders and caecilians—are closely related.

Some writers have argued that the early

Some, if not all, lissamphibians share the following characteristics. Some of these apply to the soft body parts, hence do not appear in fossils. However, the skeletal characteristics also appear in several types of Palaeozoic amphibians:^[6]

• Double or paired
  occipital condyles
• Two types of
  skin glands
  (mucous and granular)
• Fat bodies associated with gonads
• Double-channeled sensory papillae in the inner ear
• Green rods (a special type of visual cell, unknown in caecilians)
• Ribs do not encircle body. In anurans the ribs are fused to their vertebrae, except in the suborder Archaeobatrachia which still has free ribs.^[7]
• Ability to elevate the eyes (with the levator bulbi muscle)
• Forced-pump respiratory mechanism, the primitive breathing system also found in labyrinthodont amphibians^[8]
• Cylindrical centra (the main body of the vertebrae; cylindrical centra are also found in several groups of early tetrapods)
• Pedicellate teeth (the crowns of the teeth are separated from the roots by a zone of fibrous tissue; also found in some Dissorophoidea; the teeth of some fossil salamanders are not pedicellate)
• Bicuspid teeth (two
  cusps per tooth, also found in juvenile dissorophoids
  )
• Operculum (small bone in the skull, linked to shoulder girdle by the opercularis muscle; perhaps involved in hearing and balance; absent in caecilians and some salamanders, fused to the columella (ear bone) in most anurans)
• Loss of posterior skull bones (also in Microsauria and Dissorophoidea)
• Small, widely separated pterygoid bones (also found in Temnospondyli and Nectridea)
• Wide cultriform process of the parasphenoid (also found in some Microsauria (Rhynchonkos) and Lysorophia)
• Presence of ampullae of Lorenzini in some salamanders and caecilians, but never in frogs^[9][10]

Relationships and definition

The features uniting the Lissamphibia were first noted by

Currently, the two prevailing theories of lissamphibian origin are:

• Monophyletic within Temnospondyli^[15]
• Monophyletic within Lepospondyli^[3]

One of the hypotheses regarding their ancestors is that they evolved by paedomorphosis and miniaturization from early tetrapods.^[16][17]

Molecular studies of extant amphibians based on multiple-locus data favor one or the other of the monophyletic alternatives and indicate a

The stem-caecilian Funcusvermis, described in 2023, retained many dissorophoid temnospondyl features, supporting a monophyletic Lissamphibia within clade Temnospondyli.^[20]

References